This invention relates generally to an electric signal generation and transmission apparatus and method, and more particularly to an electrical signal compensation apparatus and method which compensates for distortion of an electric signal due to the varying rate of change of the signal.
Electrical signals are affected by physical conditions during transmission. The affect on the transmitted signal is dependent on a number of factors, including the frequency of the transmitted electrical signal and the transmission distance of the electrical signal. For example, a rectangular pulse will become more rounded by the low pass filter effect of a transmission wire as the frequency of the rectangular pulse increases. Digital pulse codes having spacing intervals of integer multiples of T between voltage transitions (where T is time) are attenuated more in the higher frequencies (closely spaced transitions having shorter times between transitions, such as 1T, by way of example) than in the lower frequencies (less closely spaced transitions having longer times between transitions, such as a multiple of T, by way of example).
These effects on a transmitted electrical signal are a result of the physics of the transmission system, and are therefore systematic. An electrical signal is subjected to electro-magnetic distortion during high-speed generation, during propagation within the wire, when passing through any transition position between elements in the electrical transmission system, when being coupled, for example, by an opto-electrical converting device, when being passed through a bandpass filter, or when being stored on a magnetic medium. For example, any number of specific circuits are required for launching of the electrical signal. Additionally, during generation of the signal, further signal processing generally is required to provide impedance matching to suppress reflections during transmission, for coupling and gain control for reception, for equalization to compensate for frequency dependent attenuation of the electrical signal and for smoothing the signal. Each of these signal processing circuits may imposes some degree of electro-magnetic transient distortion on the electrical signal due to the varying rate of change of the signal. Additionally, since a wire transmission line also acts as a circuit, the transmission wire itself introduces electro-magnetic distortion into the waveform.
Since these circuits form at least a part of each and every transmission of an electrical signal from a particular transmission apparatus, the affects thereof are repeatable on similar frequency signals transmitted through a similar transmission apparatus over a similar transmission distance. These affects become greater as the frequency of the electrical signal increases and as the transmission distance of the electrical signal increases. These affects may result in signals which have fast rise and fall times and a wide frequency bandwidth overshooting the desired voltage levels, resulting in ringing, or other distortions. The removal of these distortions requires additional signal processing, which may then generate further electrical distortion.
Therefore, it would be beneficial to provide an apparatus for generating and transmitting an electrical signal which can compensate for rather than suffer from the electro-magnetic transient distortion of prior art generation and transmission systems.